1. Field of the Invention
The present invention relates to a mirror fixing device for a motor employing a beam reflector. More particularly, this invention relates to a mirror fixing device for a motor employing a beam reflector that fixes a mirror with prevention of gas leakage.
2. Description of the Prior Art
Generally, a motor employing a beam reflector such as a scanner motor for use in a laser beam printer, a digital copier or the like requires a device for fixing a beam-reflecting mirror and a structure for preventing an evaporated lubricant such as a grease leaking from a motor housing.
In a conventional scanner motor 10, with reference to FIG. 1, a shaft holder 12 is provided at the central portion of a printed circuit board 11 for providing a driving current to the motor. In this holder 12, a motor shaft 13 is inserted.
A supporter 14 is mounted on one part of the printed circuit board 11. The supporter 14 supports a stator core 15 which is manufactured by press-manufacturing and laminating silicic metal plates. A coil 16 is wound on this stator core 15, and electronic components 17 mounted on the printed circuit board 11 apply a driving current to the coil 16.
Meanwhile, the motor shaft 13 is rotatably supported by bearings 18 and 18'. The upper bearing 18 is fixed by a fixing ring 20 which clamps the shaft 13 and by an elastic member 21 inserted between the upper bearing 18 and the fixing ring 20. The lower bearing 18' is fixed by the shaft holder 12 when assembled.
These bearings 18 and 18' are equipped inside a housing 22. Around the outer circumferential surface of the housing 22, a rotor yoke 23 is assembled. A magnet 24 for forming a magnetic field is attached to the end part of the rotor yoke 23. This magnet 24 rotates the rotor yoke 23 in interaction with the energized coil 16, resulting in rotation of the housing 22.
In addition, on a shoulder 25 formed around the outer surface of the housing 22, a polygon mirror 26 for reflecting a laser beam to focus an image on a photoconductive drum, is mounted. The mirror 26 rotates with an extremely high speed to line-scan an image read out from a paper on the photoconductive drum. To increase image accuracy, the reflection factor of the mirror must be secured over 99 percent, requiring a device for uniformly fixing the mirror.
To meet this requirement, the conventional motor is provided with the fixing ring 20 and elastic members 21 as shown in FIG. 1.
In addition, the bearings 18 and 18' play a role in smoothing the rotation of the housing 22 mounting the polygon mirror 26. To help this, a lubricant such as grease is necessarily applied to the bearings 18 and 18'. However, due to the high-speed bearing rotation, the lubricant is apt to be boiled and vaporized, and the vaporized lubricant gas leaks out of the housing. This leaking gas has a bad effect on neighboring parts, and particularly when adhering to the mirror, the image is severely distorted.
To avoid this problem, a device for preventing the gas leakage has been developed. Referring to FIG. 1, it can be noted that a cap 27 is put on the top opening of the housing 22. The cap 27 hermetically seals the housing 22 so as to prevent the gas from leaking.
However, such conventional devices must individually employ a fixing ring and elastic members for fixing a polygon mirror and a cap for preventing gas leakage, and this causes a complicated structure and increased work time. Accordingly, workability, productivity, and reliability are lowered, and thus the production cost are increased.